| ctf | ECMG Content Transformation File |
| cth | MegaPOV Cloth Simulation Data |
| cti | Collectorz.com Template Info File |
| ctlg | elcoCAD Catalog Data |
| ctlx | myCatalogs Database |
| ctm | CrazyTalk Model Data |
| ctmdpi | MRMC Rate Matrix Data |
| ctn | CADTERNS Sloper |
| ctpx | Microvellum Cut Parts File |
| ctr | BrainVoyager QX Contrast Data |
| cts | CrazyTalk Script |
| cts | GodswMobile Contacts Transfer Backup |
| ctt | ETCBC Coded Text Tabulated Data |
| ctt | MSN Messenger Contact List |
| ctx | CyberTracker Exported Data |
| ctz | Cherrytree Password Protected Data |
| cu | CU-SeeMe Data |
| cu | my Knowledge Explorer Change Unit |
| cu1 | PhotoLine 4 Curve Data |
| cu3 | PhotoLine 4 Curve Data |
| cub | Gaussian Cube Data |
| cub | ISIS 2 Cube |
| cube | Gaussian Cube Data |
| cuce | CU-SeeMe Data |
| cud | ChmUpDate Data |
| cudt | ClarisWorks User Dictionary Data |
| cuix | Autodesk AutoCAD Custom User Interface |
| cul | Windows Cursor Library |
| cup | Naviter SeeYou Waypoint Data |
| cur | Oasys T/HIS Curve File |
| cursorfx | CursorFX Theme |
| curv | Genetica Mathematical Curve |
| curve | ANSYS TurboGrid Curve File |
| curxptheme | CursorXP Theme |
| cus | Autodesk AutoCAD Custom Dictionary |